Recent attention has focused on high aspect ratio carbon micro-electro-mechanical-systems (C-MEMS) because of the many applications that can be envisioned for C-MEMS such as micro-electrodes in electrochemical sensors and miniaturized energy storage/energy conversion devices. Some important C-MEMS properties include: the material has a very wide electrochemical stability window, it exhibits excellent biocompatibility, is low cost, is very reproducible, very fine geometries can be defined as opposed to the more traditionally used printing of carbon inks, a wide range of resistivities and mechanical properties can be obtained, and the surface of this very chemically inert material is easy to derivatize. The material has particular importance in bioMEMS applications including DNA arrays, glucose sensors, and micro-batteries. Further, suspended micro/nano carbon structures exhibit a wide electrochemical stability window and are also free of Van-der-waal's interactions with the substrate which makes them interesting for integration in mechanical, electrical, and electromechanical measurements. One of the biggest advantages of suspended micro/nano carbon structures is the high surface to volume ratio.
Yet, microfabrication of C-MEMS carbon structures using current processing technology, such as focus ion beam (FIB) and reactive ion etching (RIE), tends to be time consuming and expensive. Low feature resolution, and poor repeatability of the carbon composition as well as the widely varying properties of the resulting devices limits the application of screen printing of commercial carbon inks for C-MEMS. One promising C-MEMS microfabrication technique, however, is based on the pyrolysis of photo-patternable resists (photoresists) at different temperatures and different ambient atmospheres. The advantage of using photoresists as the starting material for the microfabrication of various carbon structures is that the photoresists can be very finely patterned by photolithography techniques and hence a wide variety of repeatable shapes are possible. Moreover different temperature treatments result in different resistivities and mechanical properties. Therefore, in comparison to techniques using other substances, methods using photoresist allow for superior repeatability of shape and dimension.
Most pyrolyzed photoresist structures described in the literature today concern carbon features derived from positive photoresist and are very low aspect ratio. The fabrication of high aspect ratio and dense C-MEMS patterns is a challenging problem because with increasing photoresist thickness, the requirements of any lithography process increase exponentially. Basically, it is very difficult to design a thick positive tone photoresist chemistry to achieve the necessary transparency and to achieve reasonable exposure doses while maintaining excellent sidewall angles. The LIGA process in which PMMA resist is exposed with an x-ray source has produced structures of the order of 1 mm in height and aspect ratios of over 50. However, this technique requires an expensive synchrotron source, hence the motivation for cheaper and easier processes.
Thus, it would be desirable to provide improved systems and methods for the controlled fabrication of suspended carbon micro/nano structures in desired positions and with the desired shape and dimension.